General Betting Math
Fractional Kelly Calculator
Reduce the full Kelly recommendation to a selected fraction. The page also explains why a personal exposure cap can be lower than the mathematical stake.
Enter one event snapshot
Preserve source precision; represent uncertainty with another case rather than extra rounding.
What this page can answer
This page calculates Fractional Kelly stake from the visible Bankroll and Estimated win probability entries. The output applies only to the scenario and market boundaries stated on the form.
Reading the formula
The recommendation follows a policy under the entered odds and win rate.
Fractional sizing or a cap can reduce sensitivity to error.
Within this calculation, use a separate scenario for a plausible upper or lower assumption.
Input scope and units
- For fractional Kelly stake, Bankroll represents current betting bankroll.
- In the current scenario, use a current source for Estimated win probability. Here it means your probability estimate.
- American odds records enter positive or negative American odds.
- Keep Kelly fraction to use on the event basis defined here: share of the full Kelly recommendation.
- Lower estimated win probability before accepting the stake or growth path.
- Compare the baseline with a capped or fractional policy.
- A longer losing-sequence case provides a cautious boundary.
Conditions to review
In this model, cash, restricted credit, gross return, and net profit may require separate accounting.
After documenting fractional Kelly stake, the Kelly Criterion can answer another question.
As a practical check, these numbers demonstrate how fields flow into the answer.
Bankroll is set to $940 for this worked case.
Estimated win probability is set to 61.6% for this worked case.
American odds is set to -100 for this worked case.
Kelly fraction to use is set to 26% for this worked case.
Applying the Fractional Kelly rule: stake = bankroll × full Kelly fraction × selected fraction.
- Full Kelly fraction: 23.20%
- Applied fraction: 26.00%
- Estimated edge: 23.20%
Using the result cautiously
Sizing assumes the edge persists across comparable opportunities.
Personal limits remain outside the optimum.
A separate dutching scenario belongs on Dutching; compare results only after matching participant and period.
When to update the page
Reasons to calculate again
- A smaller fraction reduces volatility but cannot correct a poor probability estimate.
- On this page, review promotion terms, limits, push treatment, void rules, and whether stake is returned before comparing profit.
- For this comparison, a value from another event may use the correct unit while answering a different question.
Input and settlement questions
Does Fractional Kelly Calculator retrieve current odds or participant news?
In this model, do extra decimal places make fractional Kelly stake more reliable?
Treat the revised situation independently: compare Fractional Kelly stake only after Bankroll and Estimated win probability have been tied to one clearly named market.
Before using the result, should bankroll be rounded before entry for Fractional Kelly?
For this market, which grading rules matter here for Fractional Kelly?
For a defensible answer, start another case with Bankroll and Estimated win probability measured for that exact period; do not rescale Fractional Kelly stake.
At this stage, what if the market covers a different period for Fractional Kelly?
Create a separate Fractional Kelly case for that period. Re-source Estimated win probability and American odds for the new scope instead of scaling Fractional Kelly stake mechanically.